1. Field of the Invention
This invention relates to a low-temperature calcined inorganic composition which can be simultaneously calcined with a low-resistance conductor such as Au, Ag and Cu. In particular, this invention relates to a low-temperature calcined glass ceramic which has a low dielectric constant and a low dielectric loss at a frequency in microwave and millimeter-wave ranges and which is suitable as an insulating layer in a multilayer wiring board for a microwave or millimeter-wave circuit.
2. Description of the Prior Art
A low-temperature calcined glass ceramic multilayer wiring board has been developed as an effective measure for improving performance of an electronic equipment because it permits a multilayered wiring, a higher density with a fine wiring and a miniaturized wiring; a low-resistance conductor such as Au, Ag and Cu can be selected as a wiring material; and the dielectric constant of an insulating layer may be lowered to allow a signal to be quickly transferred. In addition, a radio-frequency analogue circuit can be electromagnetically shielded because of a contact pattern of conductor plane and a high-density layout of cavity structures and via holes. Therefore, various elements such as a transmitter and receiver module and a DC or RF circuit may be integrated, which leads to miniaturization and performance improvement. Furthermore, a module mounted with multiple MMICs may be miniaturized and improved in its performance. Thus, the wiring board has been developed for use in, for example, a module for a communication device including a high-frequency analogue circuit in a microwave range.
In the field of high-frequency communication devices such as those for mobile communication and satellite communication, it is expected to use a system involving a super high-frequency range such as microwave and millimeter wave in a variety of applications. In the field of communication devices comprising a high-frequency analogue circuit, it is expected to use systems involving not only a microwave band but also a millimeter wave band, a further higher frequency range. In a module equipped with such an analogue circuit involving a super high-frequency range, it is essential to reduce a signal transmission loss. Therefore, for a glass ceramic type of multilayer wiring board, it is needed to minimize a dielectric loss of an insulating material and a resistance of a conductor.
An object of this invention is to provide a low-temperature calcined glass ceramic which can be calcined at a temperature below 1000xc2x0 C., i.e., can be calcined simultaneously with a low-resistance conductor such as Au, Ag and Cu for internal mounting or multilayering, and which is suitable for an insulating layer in a multiple layer wiring board equipped with a high-frequency analogue circuit with a low dielectric constant and a low dielectric loss at a frequency within microwave and millimeter wave ranges.
We have intensely investigated a variety of glass compositions in an attempt to solve the problems in a conventional low-temperature calcined glass ceramic, and have found that an SiO2xe2x80x94B2O3xe2x80x94CaOxe2x80x94Al2O3 glass with a certain range of composition has a low glass softening point, can be calcined at a temperature below 1000xc2x0 C. as a composite with various ceramics and is crystallized during a calcination process to exhibit a low dielectric constant and a low dielectric loss, and that an SiO2xe2x80x94CaOxe2x80x94Al2O3 glass with a certain range of composition, as a composite with various ceramics or alone, can be calcined at a temperature below 1000xc2x0 C. and is crystallized during a calcination process to exhibit a low dielectric constant and a low dielectric loss.
This invention provides:
(1) A low-temperature calcined glass ceramic consisting of 50 to 100 wt % of glass powder and 0 to 50 wt % of ceramic powder, where the glass powder has an oxide-converted composition of 35 to 65 wt % of SiO2, 5 to 35 wt % of B2O3, 2 to 20 wt % of CaO, 5 to 25 wt % of Al2O3 where the ratio of CaO to Al2O3 is 1/1 to 1/2.5, 0.5 to 5 wt % of TiO2, 0.5 to 5 wt % of ZrO2, 0.5 to 5 wt % of ZnO, 0 to 5 wt % of MgO, 0 to 5 wt % of SrO, 0 to 5 wt % of BaO and 0 to 1 wt % of a group 1A element oxide; and is densified during calcination at 850 to 1000xc2x0 C.;
(2) A low-temperature calcined glass ceramic described in (1), where the group 1A element oxide is at least one selected from the group consisting of Na2O, K2O and Li2O;
(3) A low-temperature calcined glass ceramic described in (1) or (2), where alumina is precipitated during the calcination process;
(4) A low-temperature calcined glass ceramic described in (1) or (2), where CaAl2SiO6 is precipitated during the calcination process;
(5) A low-temperature calcined glass ceramic described in any of (1) to (4), where the ceramic powder is at least one selected from the group consisting of alumina, silica, mullite, cordierite and forsterite;
(6) A low-temperature calcined glass ceramic which is an SiO2xe2x80x94CaOxe2x80x94Al2O3 glass having an oxide-converted composition of 10 to 45 wt % of SiO2, 20 to 50 wt % of CaO, 20 to 45 wt % of Al2O3, 0.1 to 5 wt % of MgO, 0.1 to 5 wt % of SrO, 0.1 to 5 wt % of BaO, 0.1 to 5 wt % of TiO2, 0.1 to 5 wt % of ZnO, 0.1 to 5 wt % of ZrO2 and 0 to 3 wt % of a group 1A element oxide; and is densified during calcination at 800 to 1000xc2x0 C.;
(7) A low-temperature calcined glass ceramic which is a composite comprising ceramic particles dispersed in an SiO2xe2x80x94CaOxe2x80x94Al2O3 glass having an oxide-converted composition of 10 to 45 wt % of SiO2, 20 to 50 wt % of CaO, 20 to 45 wt % of Al2O3, 0.1 to 5 wt % of MgO, 0.1 to 5 wt % of SrO, 0.1 to 5 wt % of BaO, 0.1 to 5 wt % of TiO2, 0.1 to 5 wt % of ZnO, 0.1 to 5 wt % of ZrO2 and 0 to 3 wt % of a group 1A element oxide; and is densified during calcination at 800 to 1000xc2x0 C.;
(8) A low-temperature calcined glass ceramic described in (6) or (7), where the group 1A element oxide is at least one selected from the group consisting of Na2O, K2O and Li2O;
(9) A low-temperature calcined glass ceramic described in (7) or (8), where the rate of the ceramic particles in the composite is 10 to 50 wt %;
(10) A low-temperature calcined glass ceramic described in any of (7) to (9), where the ceramic particles are particles of at least one selected from Al2O3(alumina), SiO2(silica), Mg2Al4Si5O18(Cordierite), Mg2SiO4(Forsterite) and Al6Si2O13(Mullite);
(11) A low-temperature calcined glass ceramic described in any of (6) to (10), where at least one of the crystals of CaAl2SiO6, Ca3Si2O7(Rankinite), CaSiO3(Wollastonite) and Al6Si2O13(Mullite) is precipitated;
(12) A process for manufacturing a low-temperature calcined glass ceramic, comprising the steps of:
(A) film deposition where a green sheet is prepared from a mixed powder consisting of 50 to 100 wt % of SiO2xe2x80x94CaOxe2x80x94Al2O3 glass powder and 0 to 50 wt % of ceramic powder;
(B) lamination where the green sheet is piled up and is then hot-pressed to give a laminate;
(C) calcination where the laminate from the above step is calcined at a temperature of 800 to 1000xc2x0 C. to give a sintered compact, characterized in that the glass has an oxide-converted composition of 10 to 45 wt % of SiO2, 20 to 50 wt % of CaO, 20 to 45 wt % of Al2O3, 0.1 to 5 wt % of MgO, 0.1 to 5 wt % of SrO, 0.1 to 5 wt % of BaO, 0.1 to 5 wt % of TiO2, 0.1 to 5 wt % of ZnO, 0.1 to 5 wt % of ZrO2 and 0 to 3 wt % of a group 1A element oxide;
(13) A process for manufacturing a low-temperature calcined glass ceramic described in (12), where the group 1A element oxide is at least one selected from the group consisting of Na2O, K2O and Li2O;
(14) A process for manufacturing a low-temperature calcined glass ceramic described in (12) or (13), where the ceramic particles are particles of at least one selected from Al2O3(Alumina), SiO2(Silica), Mg2Al4Si5O18(Cordierite), Mg2SiO4(Forsterite), CaAl2SiO7, Ca3Si2O7(Rankinite), CaSiO3(Wollastonite) and Al6Si2O13(Mullite);
(15) A process for manufacturing a low-temperature calcined glass ceramic described in any of (12) to (14), where during the calcination at least one of the crystals of CaAl2SiO6, Ca3Si2O7(Rankinite), CaSiO3(Wollastonite) and Al6Si2O13(Mullite) is precipitated.
The low-temperature calcined glass ceramic of this invention allows a multilayer wiring to be made of a low-resistance conductor, and thus provides a multilayer wiring board with excellent high-frequency properties.
A first embodiment of this invention will be described.
The first low-temperature calcined glass ceramic of this invention consists of 50 to 100 wt % of glass powder and 0 to 50 wt % of ceramic powder, where the glass powder has an oxide-converted composition of 35 to 65 wt % of SiO2, 5 to 35 wt % of B2O3, 2 to 20 wt % of CaO, 5 to 25 wt % of Al2O3 where the ratio of CaO to Al2O3 is 1/1 to 1/2.5, 0.5 to 5 wt % of TiO2, 0.5 to 5 wt % of ZrO2, 0.5 to 5 wt % of ZnO, 0 to 5 wt % of MgO, 0 to 5 wt % of SrO, 0 to 5 wt % of BaO and 0 to 1 wt % of the total of group 1A element oxides including Na2O, K2O and Li2O; and where mainly alumina and CaAl2SiO6 are precipitated during calcination.
A composition consisting of, as converted to an oxide, 35 to 65 wt % of SiO2, 5 to 35 wt % of B2O3, 2 to 20 wt % of CaO, 5 to 25 wt % of Al2O3 where the ratio of CaO to Al2O3 is 1/1 to 1/2.5 precipitates a crystal phase consisting of alumina and CaAl2SiO6 during calcination, to give a sintered compact exhibiting a low dielectric constant and a low dielectric loss. In particular, a composition consisting of 35 to 65 wt % of SiO2, 5 to 30 wt % of B2O3, 2 to 17.5 wt % of CaO, 5 to 17.5 wt % of Al2O3 where the ratio of CaO to Al2O3 is 1/1 to 1/2.5 is preferable because it has a relatively lower glass softening point and exhibits a low dielectric constant and a low dielectric loss. Said composition, however, has a considerably high glass softening point, which makes sintering at a temperature below 1000xc2x0 C. difficult.
Adding 0.5 to 5 wt % of TiO2, 0.5 to 5 wt % of ZrO2 and 0.5 to 5 wt % of ZnO to the composition may lower a glass softening point without significantly deteriorating dielectric properties. It is undesirable to add any of these additives in more than 5 wt % due to significant deterioration of dielectric properties, while less than 0.5 wt % of any of these additives may not be very effective. One to three wt % of TiO2, 1 to 3 wt % of ZrO2 and 1 to 3 wt % of ZnO are added in the light of the effect of lowering a glass softening point while maintaining a low dielectric constant and a low dielectric loss. It is effective to add 0 to 5 wt % of MgO, 0 to 5 wt % of SrO and 0 to 5 wt % of BaO because they may, as with the above additives, lower a glass softening point. Adding more than 5 wt % of these is undesirable due to significantly deteriorating dielectric properties. It is preferable to add 0.5 to 3 wt % of MgO, 0.5 to 3 wt % of SrO and 0.5 to 3 wt % of BaO in the light of the effect of lowering a glass softening point while maintaining a low dielectric constant and a low dielectric loss. To further lower a glass softening point, it may be effective to add 0 to 1 wt % of Na2O, K2O and/or Li2O. It is undesirable to add Na2O, K2O and/or Li2O in more than 1 wt % as a total due to increase of dielectric loss.
Thus, a glass composition consisting of 35 to 65 wt % of SiO2, 5 to 35 wt % of B2O3, 2 to 20 wt % of CaO, 5 to 25 wt % of Al2O3 where the ratio of CaO to Al2O3 is 1/1 to 1/2.5, 0.5 to 5 wt % of TiO2, 0.5 to 5 wt % of ZrO2, 0.5 to 5 wt % of ZnO, 0 to 5 wt % of MgO, 0 to 5 wt % of SrO, 0 to 5 wt % of BaO and 0 to 1 wt % of the total of group 1A element oxides including Na2O, K2O and Li2O, preferably consisting of 35 to 65 wt % of SiO2, 5 to 30 wt % of B2O3, 2 to 17.5 wt % of CaO, 5 to 17.5 wt % of Al2O3 where the ratio of CaO to Al2O3 is 1/1 to 1/2.5, 1 to 3 wt % of TiO2, 1 to 3 wt % of ZrO2, 1 to 3 wt % of ZnO, 0.5 to 3 wt % of MgO, 0.5 to 3 wt % of SrO and 0.5 to 3 wt % of BaO has a low glass softening point, and a glass ceramic consisting of 50 to 100 wt % of the glass powder and 0 to 50 wt % of ceramic powder can be calcined at a temperature below 1000xc2x0 C. Therefore, the glass ceramic allows a multiple layer wiring to be formed by simultaneous calcination with a low-resistance conductor such as Au, Ag and Cu. and may achieve a low dielectric constant and a low dielectric loss in both microwave and millimeter wave frequency bands.
The ceramic powder may be any of alumina, silica, mullite, cordierite, forsterite and so forth, but preferably a material with a low dielectric constant and a low dielectric loss is selected for avoiding deterioration of dielectric properties. A composite of glass and ceramic consisting of glass and ceramic is preferable because it may improve strength. More than 50 wt % of the rate of the ceramic powder is undesirable because it requires a higher calcination temperature. It is preferable to use 5 to 30 wt % of ceramic powder in the light of dielectric properties, strength and a calcination temperature.
The second embodiment of this invention will be described.
The second low-temperature calcined glass ceramic of this invention is an SiO2xe2x80x94CaOxe2x80x94Al2O3 glass or a composite comprising ceramic particles dispersed in the glass, where the glass has an oxide-converted composition of 10 to 45 wt % of SiO2, 20 to 50 wt % of CaO, 20 to 45 wt % of Al2O3, 0.1 to 5 wt % of MgO, 0.1 to 5 wt % of SrO, 0.1 to 5 wt % of BaO, 0.1 to 5 wt % of TiO2, 0.1 to 5 wt % of ZnO, 0.1 to 5 wt % of ZrO2 and 0 to 3 wt % of a group 1A element oxide. An SiO2xe2x80x94CaOxe2x80x94Al2O3 glass having such a composition can be calcined at a temperature of 800 to 1000xc2x0 C., alone or as a composite with ceramic particles, permitting a multilayer wiring board to be prepared using a low melting-point and low resistance conductor such as Au, Ag and Cu as an internal-layer wiring material. An SiO2xe2x80x94CaOxe2x80x94Al2O3 glass having such a composition exhibits a low dielectric constant and a low dielectric loss. It is, therefore, suitable for an insulating layer in a multilayer wiring board for a high-frequency circuit.
The above composition will be described in detail. A glass having a composition within the above range may be calcined at a temperature below 1000xc2x0 C. In particular, it is preferable for low-temperature calcination to add each of MgO, SrO, BaO, TiO2, ZnO and ZrO2 in an amount of 0.1 to 5 wt % for lowering a softening point and a temperature range in calcination. An excessive amount of these additives may, however, adversely affect a low dielectric loss which is a characteristic of a low-temperature calcined glass ceramic, leading to increase of a dielectric loss. Their individual amounts must be, therefore, below 5 wt %. On the other hand, when they are added in too small amounts, a calcination temperature range may be raised, making calcination at 1000xc2x0 C. or lower difficult. Their amounts must be, therefore, at least 0.1 wt %. In particular, it is preferable to add each of these additives in an amount of 0.5 wt % to 2 wt % both inclusive because it allows calcination temperature to be about 900xc2x0 C.
Addition of a group 1A element oxide may significantly lower a glass softening point and thus is effective for lowering a calcination temperature, but may largely increase a dielectric loss. The amount must be, therefore, below 3 wt %, preferably below 1 wt %.
A composite of the glass having the above composition with ceramic particles may be useful because material strength, a dielectric constant, a dielectric loss and a coefficient of thermal expansion can be modified by selecting ceramic particles as appropriate. The rate of ceramic particles is preferably below 50 wt %. If it is more than 50 wt %, calcination at a temperature below 1000xc2x0 C. is considerably difficult. The blending rate is preferably 10 wt % to 30 wt % both inclusive because it is effective for improving material strength. The ceramic may be selected from alumina, silica, mullite, cordierite and forsterite, and preferably a material with a low dielectric constant and a low dielectric loss in the light of preventing deterioration of dielectric properties.
A glass having the above composition precipitates the crystals of CaAl2SiO6, Ca3Si2O7(Rankinite), CaSiO3(Wollastonite) and/or Al6Si2O13(Mullite) during a calcination process at a temperature of 800 to 1000xc2x0 C. The crystals are precipitated in different ways depending on a glass composition and calcination conditions, but such precipitation itself may be effective for reducing a dielectric loss and improving material strength.
For preparation of a multilayer wiring board using the second low-temperature calcined glass ceramic of this invention, a green sheet lamination technique may be effective. In a solvent as a dispersion medium are added a glass powder having the above composition with an average particle size of some submicrons to several microns, a plasticizer and a binder, and the mixture is blended to provide a slurry. The slurry is subject to an appropriate film-forming process such as a slip casting method to give a green sheet. The particle size of the glass powder may vary depending on a calcination temperature, a shrinkage rate between before and after calcination and the amounts of different organic vehicles during preparation of the slurry, and the average particle size is preferably 1 to 3 xcexcm in the light of handling properties. When the low-temperature calcined glass ceramic is used as a composite with ceramic particles, the ceramic particles may have an average size of some submicrons to several microns. The particle size may influence a variety of factors as described in terms of the above glass powder. Particles with an average size of about 0.5 to 2 xcexcm is preferable because they are effective for improving material strength. Some elements such as a via conductor, a circuit and a cavity are formed on the green sheet. The processed green sheet is piled and then hot-pressed to be laminated. The laminate is subject to calcination at a temperature of 800 to 1000xc2x0 C. to provide a multilayer wiring board. In the calcination process, the glass having the above composition precipitates different crystals, depending on factors such as calcination conditions and a glass composition. Such precipitation allows an insulating layer to exhibit a further lower dielectric loss, a substrate to be stronger, and a multilayer wiring board to be provided, which is suitable for mounting a high frequency circuit on it.